replacing Caldwell window balances

A home owner from Beaver, Pa says:
House has 1960 Bilt_Well double hung windows. Need to replace the Caldwell window balances which are 8"by 33/4" by 1." Would any of your Anderson window balances work?
A customer submitted photo of a sash balance.
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Paul from SWISCO responded:
Caldwell has discontinued this type of balance. The Andersen box balance is a smaller box, so if you want to keep your old sashes, you will need to do some modifying. If you're interested, please tell me your sash glass size and the weight of your sash.
A home owner from Beaver, Pa, says:
Double Hung: Upper 31 1/2" by 25" app 15 pounds. Lower 38 1/2" by 25" approx 20 pounds. Extra weight is due to replacing the original glass with leaded pane windows.Weight is an approximation.

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Casey from SWISCO responded:
Our best guess is the 24-837 for the 31-1/2" x 25" sash and the 24-1033 for the 38-1/2" x 25" sash. I'm really not sure if you will be able to adapt these.
How to replace an Andersen Window Balance
How to replace an Andersen Window Balance
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